Implantable cardiac rhythm management devices are an effective treatment in managing irregular cardiac rhythms in particular patients. Implantable cardiac rhythm management devices are capable of recognizing and treating arrhythmias with a variety of therapies. To effectively deliver these therapies, however, cardiac rhythm management devices must first accurately sense and classify an episode.
In order to apply the proper therapy in responding to an episode, some cardiac rhythm management devices compare sensed cardiac signals to a previously stored “template” representing normal sinus rhythm (NSR) or other “template” frequently intended to represent the patient's NSR. Problems arise when the cardiac rhythm management device inaccurately compares a sensed cardiac complex to a stored NSR template, and as a result, misclassifies the sensed cardiac complex. The severity of this problem escalates if the cardiac rhythm management device inappropriately delivers and/or withholds therapy due to the misclassification. In illustration, when a particular group of sensed complexes are erroneously compared to a stored template because of an improper alignment to the template, a cardiac rhythm management device may mistakenly classify these sensed complexes as a mismatch and even possibly as a tachyarrhythmia.
Much of the analysis performed on cardiac signals includes sampling a cardiac signal and comparing the sampled signal to a stored template. Thus, a series of sampled signals are compared to stored data. Often a correlation analysis is performed to compare the two data sets. Typically, a number of peaks will appear in each signal. If the peaks are poorly aligned, low correlation will often result. With poor alignment, a “good” sampled signal may, in analysis, illustrate poor correlation, erroneously indicating treatment. Techniques for enabling and assuring good alignment are therefore desired.